Thermo-catalytic process for conversion of lignocellulosic biomass to fuels and chemicals: a review

Fossil fuels, the dominant source of energy in today's modern civilization has significant negative impact on global climate change.The lignocellulosic biomass can be a more sustainable replacement of fossil fuel in the production of transportation fuels and petrochemical feedstock.However, high concentration of oxygen functionalized compounds in biomass presents a major challenge in the development of biomass technology.For a biomass conversion to be efficient, achieving faster heating rate >10°C/s of the solid biomass is the key to achieve higher liquid yield and lower coke make.In the fast pyrolysis, There are again two major approaches: i. Thermal pyrolysis of biomass and subsequent separate treatment of bio-oil ii.Combining catalytic fast pyrolysis within-situ upgrading of the generated bio oil in a single reactor system.The bio-oil produced by the first approach can be co-processed in an existing secondary conversion unit of a refinery, such as FCC or hydroprocessing.Fluidized bed has proven to be the best reactor for biomass pyrolysis in both the approaches i.e. thermal or catalytic, mainly due to the excellent heat/ mass transfer rate and high solid handling flexibility of fluidized system.However, the major challenges, following the second approach i.e. the catalytic fast pyrolysis is to achieve high degree of de-oxygenation, while retaining maximum C and H within the liquid.Good de-oxygenation >70% is essential to get a stable liquid product with acceptable corrosivity.The other challenge is the fast deactivation of catalyst due to the impurities present in biomass, specifically K > 5 ppm.Upgrading the bio oil quality to achieve the high standard of transportation fuel requires costly multi step high pressure hydroprocessing system.Thus the new advent is to directly produce olefins and aromatics from biomass which not only helps to enhance the product value but also greatly minimizes the need of too much hydrotreating Figure 1.